Cell cycle parameters in human colon: comparison between primary and recurrent adenocarcinomas, benign polyps and adjacent unaffected mucosa

Expression of Musashi-1 in human normal colon crypt cells: a possible stem cell marker of human colon epithelium

Musashi has been identified as an RNA-binding protein thought to be involved in asymmetric divisions during Drosophila neural development. To analyze expression patterns of mammalian Musashi homolog Musashi-1 in human normal colon crypt, 155 colon crypts separated from biopsy specimens of normal colonic mucosa were evaluated. Specimens were fixed, microdissected to isolate a few crypts, immunostained with anti-Musashi-1 antibody (14H1), and examined under confocal laser scan microscopy. The number of Musashi-1-positive cells in each crypt was 19.0 +/- 7.53 (mean +/- SD). Most Musashi-1 positive cells were located at the crypt base, between cell positions 1 and 10. Distribution of Musashi-1-positive cells corresponded with that of stem cells, as outlined in previous reports, implying that Musashi-1 is a key control element of asymmetrical division within the colon crypt. This is the first report outlining expression of Musashi-1 in human colon crypt cells.

Growth kinetics of colorectal adenoma-carcinoma sequence: an immunohistochemical study of proliferating cell nuclear antigen expression

Tumorigenesis is a multistep process that begins with the abrogation of normal controls of cell proliferation. The authors examined the in vitro growth kinetics and compartment shift through the adenoma-carcinoma sequence of the human colon by determining the labelling indexes of proliferating cell nuclear antigen (PCNA) in normal mucosae (n = 10), adenomas (n = 88), and carcinomas (n = 20). Carcinoma cells had a significantly higher PCNA index than adenomas or control specimens (P = .0001). There also was a difference in the PCNA index between the histological subtypes of adenomas (P = .03), whereas no significant difference was observed for dysplastic grade, tumor size, or location (P > .1). Tubular and tubulovillous adenomas, adenomas with mild dysplasia, small (< 10 mm) adenomas, and proximally located adenomas revealed shift of cell proliferation toward the middle portion of the colonic glands. The PCNA in the villous, moderate or severe dysplastic, larger or distally located adenomas appeared to be diffuse (P = .04, 0.02, 0.07, and 0.06, respectively). In addition, the transitional mucosa neighboring carcinoma showed an elevation of the mean PCNA index together with an upward shift of cell proliferation compared with the controls (P = .03). These results suggest a stepwise increment of proliferating activity with compartment shift of the proliferating zone through the adenoma-carcinoma sequence. The information essentially supports contemporary understanding of the carcinogenic processes in the human colon.

Depressed adenoma of the colorectum: analysis of proliferative activity using immunohistochemical staining for proliferating cell nuclear antigen (PCNA)

Recently, depressed adenomas (DA) of the colorectum have been frequently detected in Japan. The natural history and carcinogenesis of these DA remain unclear. The histological features and cell kinetics of 13 DA were analyzed, using proliferating cell nuclear antigen (PCNA), and compared with 24 non-depressed adenomas (NDA), 12 non-neoplastic mucosa and 12 adenocarcinomas. The DA had a characteristic architecture when compared with the NDA, as demonstrated by a crowded collection of adenomatous tubules with small diameters. The adenomatous tubules tended to occupy the full thickness of the lamina propria at the center with superficial growth to the periphery. The PCNA-positive cells were mostly restricted to the lower half of the crypts in the non-neoplastic mucosa, and were distributed predominantly across the upper half area of the crypts in both the DA and NDA, whereas they were randomly distributed across any area in the adenocarcinomas. The mean labeling index of PCNA in the DA (43.2%) was significantly higher than that in the non-neoplastic mucosa (26.5%) and NDA (29.3%), but lower than that in the intramucosal component of the adenocarcinomas (70.0%). The DA should be seriously considered as a precancerous lesion because of its unusual histologic architecture and high proliferative activity.

Kinetic changes and experimental carcinogenesis after Billroth I and II gastrectomy

To determine the risk of gastric remnant cancer according to the type of surgical reconstruction, the distal two-thirds of the glandular stomach was resected in male Wistar rats, followed by gastroduodenostomy (Billroth I anastomosis) or gastrojejunostomy (Billroth II anastomosis). No carcinogens were given and the animals were killed 50 weeks after operation. No cancers developed in 22 rats undergoing Billroth I gastrectomy, but five of 24 with Billroth II anastomosis had adenocarcinoma (P < 0.05). All carcinomas were confined to the stoma. Animals with Billroth II anastomosis had a more advanced grade of mucosal atrophy at the stoma, with a higher incidence of cystic dilatation, submucosal adenocystic proliferation and pseudopyloric metaplasia (P < 0.05). Cell kinetics in the stomal mucosa after Billroth II gastrectomy showed an increased cell count in the proliferative zone, longer duration of S phase and increased cell cycle time (P < 0.05). These results suggest that Billroth II gastrectomy carries a greater risk of cancer than the Billroth I procedure.

Diagnosis of gastric adenoma versus early gastric cancer by bromodeoxyuridine immunohistochemistry from gastric biopsy specimen

Differentiation between gastric adenomas and type IIa early gastric cancer by macroscopic and histologic examinations is often difficult. This study has shown that there are differences in the distribution of S-phase cells in these two types of tumour, and these differences can be exploited to differentiate between them. The distribution of S-phase cells was assessed by Bromodeoxyuridine (BrdU) immunohistochemistry using an in vitro BrdU-labelling method. Biopsy specimens were obtained from 27 lesions (12 adenomas and 15 type IIa early gastric cancers), and the distributions of BrdU-labelled cells in the tumour thickness as well as in the superficial layer of the tumour were determined. Significant difference was seen in the labelling of the two tumour types with regard to both these parameters. Using the criteria of BrdU immunohistochemistry, the accuracy of differentiation between gastric adenomas and cancers was 88.9%. Therefore, it is concluded in this study that in vitro BrdU labelling is a useful method of diagnosing gastric adenomas and cancers.

Cell cycle parameters and DNA ploidy in colorectal carcinomas

Seven patients with colorectal adenocarcinoma and one with squamous cell carcinoma of anorectal region were infused preoperatively with iododeoxyuridine (IUdR) and bromodeoxyuridine (BrdU) in sequence (100 mg/m2 x 1 hr each with 1-hr interval in between) to label S-phase cells. The tumor biopsy specimens were embedded in glycol-methacrylate and 2-microns thick sections were treated with two monoclonal antibodies which permitted the identification of cells which incorporated IUdR only, BrdU only, both IUdR and BrdU, or neither IUdR or BrdU. The labeling index of tumors varied from 17.3 to 35.6% (mean = 25.78 +/- 6.162), duration of S-phase ranged from 14.0 to 23.9 hr (mean = 18.73 +/- 3.712), and total cell cycle time ranged from 39.4 to 123.4 hr (mean = 76.78 +/- 24.165). The architecture of the tumor was well preserved and a variable number of DNA synthesizing mononuclear cells were identified within and around the tumor. Image analysis of Feulgen-stained smears of the tumors was done to measure the DNA content of seven tumor samples. Each tumor was found to be hyperdiploid with multiple modal values. The studies described here demonstrate the feasibility of performing cell cycle kinetic measurements on gastrointestinal tumors which have been labeled in vivo. The ability to perform these measurements on tumor biopsies allows the avoidance of artifacts introduced when solid tumors are disaggregated in vitro for study.

Morphology and modes of cell proliferation in earliest signet-ring-cell carcinomas induced in canine stomachs by N-ethyl-N'-nitro-N-nitrosoguanidine

Signet-ring-cell carcinomas were induced in the stomach of 12 beagle dogs by p.o. administration of N-ethyl-N'-nitro-N-nitrosoguanidine (ENNG), and the morphology and modes of cell proliferation in an incipient stage of cancer growth were studied with bromodeoxyuridine (BrdUrd) incorporation. From 5 to 27 months after the completion of 8 months' carcinogen treatment, minute carcinomas were found in the stomachs of 9 dogs. Before sacrifice, the dogs were given a single or repeated i.v. injections of BrdUrd for 1-3 days. Minute signet-ring-cell carcinomas were found to form a layered structure, in which the cancer cells proliferated in the lamina propria at the gland-neck level and differentiated to postmitotic signet-ring cells at the upper and lower levels of the mucosa. From repeated injections of BrdUrd, the time required for all the proliferative cells to be labelled with BrdUrd (reflecting the maximum cell-cycle time) was estimated to be 1.7 days for the normal glands, and 2.7 days for minute signet-ring-cell carcinomas. From the labelling index with BrdUrd as well as from the morphology, earliest carcinomas were identified in the single gland. There remained atrophic normal epithelium commonly in the single-gland lesions. Proliferative atypical cells appeared to be shed into the stroma passively through the atrophy and subsequent collapse of the gland rather than through active invasion. This may be a reason why cancer cells in minute signet-ring cell carcinomas preserved the normal pattern of cell renewal movement to form the layered structure.

Proliferation characteristics of human colorectal carcinomas measured in vivo

The cell proliferation kinetics of 100 human colonic and rectal adenocarcinomas have been studied in vivo by bromodeoxyuridine infusion and multiparameter flow cytometry. A total of 97 patients, three with synchronous tumours, consented to receive a single bolus dose of 250 mg between 2.4 and 16 h before curative or palliative surgery. By this method, the ploidy pattern, the total and aneuploid labelling indices (LI), the S phase duration (Ts) and the potential doubling time (Tpot) can be estimated. Of the tumours 48 were diploid and 52 were aneuploid. The mean and median total LI of 100 tumours were 9.0 per cent (range 0.7-22.2 per cent). The mean aneuploid LI was 12.1 per cent (median 12.0 per cent, range 2.0-25.5 per cent), and was significantly higher than the total LI (P = 0.01). The labelling index alone is not a sufficient indicator of proliferation, because the Ts also varies within and between tumours. The intertumour range of the Ts varied from 4.0 to 28.6 h. The mean was 14.1 h and the median was 13.1 h. The mean Tpot was 5.9 days (median 3.9 days) with a range of 1.7-21.4 days. No correlation was found between any kinetic parameters and the Dukes' classification or histological classification. The correlation between proliferation and prognosis will be established in due course.

Characterization of human colorectal mucosa, polyps, and cancers by means of computerized morphonuclear image analyses

Fifty-eight Feulgen-stained imprint smears from freshly resected colorectal tissue were analyzed by means of a SAMBA 200 cell image processor to establish a quantitative grading of their evolution from normal to malignant mucosa on the basis of 15 morphonuclear parameters relative to morphometry (nuclear size), densitometry (DNA content), and texture (chromatin pattern). The colorectal samples belonged to six groups: normal mucosa from patients without (Group 1) or with (Group 2) colorectal cancer, adenomas (Group 3), and cancers corresponding to the three stages of the Dukes' classification (Groups 4 to 6). Results indicated that analysis of the morphonuclear parameters computed on 250 to 300 nuclei/cases objectively and quantitatively showed the adenoma-cancer sequence. This need for only a small number of nuclei to assess a highly efficient analysis created a preoperative investigative tool using cytologic smears during endoscopy. The authors also made preliminary data banks for objective and reproducible grading of unknown cases by comparisons (discriminant analyses) with their contents. This approach must be validated prospectively on a large series of cases to furnish a system for colorectal malignancy diagnosis.

In vivo determinations of labelling index of metastatic colorectal carcinoma and normal colonic mucosa using intravenous infusions of bromodeoxyuridine

In vivo determination of the labelling index of metastatic colon carcinoma was performed in 14 patients following intravenous infusion of bromodeoxyuridine (BrdU), at doses of 100 and 50 mg/M2. No toxicity was seen. Labelled cells were detected by an immunohistochemical technique using a monoclonal antibody to BrdU. Labelling was uniform and highly specific with good preservation of morphology. Labelling index values ranged from 15.0-40.6% for metastatic lesions and 3.6%-20% for normal colonic mucosa, with mean values of 24% and 11%, respectively. This represents a useful new method for in vivo labelling index determination in solid tumors.

Immunohistochemical study of epithelial cell proliferation in hyperplastic polyps, adenomas, and adenocarcinomas of the large bowel

A monoclonal antibody to bromodeoxyuridine was used in tissue specimens previously incubated with bromodeoxyuridine to show S-phase cells by immunohistochemical technique. Biopsy specimens of normal mucosa (n = 10), hyperplastic polyps (n = 10), adenomas with low-grade dysplasia (n = 20), adenomas with high-grade dysplasia (n = 10), and invasive adenocarcinomas (n = 10) of the large bowel were studied. Labeling index and cell proliferative patterns were analyzed. No statistically significant difference was found in labeling index between normal mucosa and hyperplastic polyps or between adenomas with high-grade dysplasia and adenocarcinomas. The labeling index was significantly lower in normal mucosa and in hyperplastic polyps than in adenomas and adenocarcinomas (p less than 0.001). The difference in labeling index between adenomas with high-grade dysplasia and low-grade dysplasia was also statistically significant (0.01 less than p less than 0.05). In normal mucosa and in hyperplastic polyps the proliferative zone was confined to the lower two-thirds of the crypt; no kinetic activity was found in the upper portions of the crypt or in surface epithelium. In adenomas the labeled cells were either present in the upper third or scattered along the whole axis of the crypt and in the surface epithelium. Labeling patterns in invasive carcinomas were similar to those observed in adenomas with high-grade dysplasia. The difference in proliferative patterns between hyperplastic polyps and adenomas supports a different significance of the two polypoid lesions in the histogenesis of large bowel cancer; our results confirm the subsequent steps of the adenoma-carcinoma sequence. Immunohistochemical labeling patterns observed with monoclonal antibody to bromodeoxyuridine in polypoid and cancer lesions of the large bowel are similar to those described by autoradiographic studies.

Cell kinetic indicators of premalignant stages of colorectal cancer

Using an in vitro double labeling technique with two different levels of 3H-thymidine, the duration of the phase of DNA synthesis (S) and the labeling index (LI) were measured in the colorectal mucosa of three groups of patients: patients with colorectal neoplasms (adenomas and/or adenocarcinomas), patients with inflammatory bowel disease, and a control group of patients without gastrointestinal pathology. In those patients with colorectal neoplasms, samples were obtained from both the neoplastic mucosa and from the normal appearing mucosa at various distances from the lesions. One-way analyses of variance were used to test the equality of mean S-phase duration and LI in the various types of tissues. S-phase duration was significantly longer in the tumor than in the unaffected mucosa of patients with adenocarcinoma (18.65 hours +/- 2.3 versus 10.13 hours +/- 1.26 P less than 0.0001). However, S-phase duration was significantly longer in the unaffected mucosa of cancer patients than in the mucosa of patients without gastrointestinal pathology (10.58 hours +/- 1.84 versus 7.91 hours +/- 0.46, P = 0.013). Similarly, LI was significantly higher in the unaffected mucosa of patients with adenoma and adenocarcinoma than in the mucosa of patients without gastrointestinal pathology (19.1% +/- 3.0 versus 9.5% +/- 2.2, P less than 0.0001). There was a highly significant trend to a progressive increase of LI from flat histologically normal appearing mucosas to inflammatory mucosas, adenomas, and adenocarcinomas (P less than 0.0001). These results suggest that increased S-phase duration is specifically related to cancer. In mucosa without histologic sign of malignancy, an increased S-phase duration would indicate that the malignant process has started. An increased LI would appear to relate to the selective advantage that rapidly proliferating cells hold over less proliferating ones.

Proliferative pattern of urothelial bladder cancer and urothelial atypias

For early diagnosis of urinary bladder tumors, autoradiographic, cytological, and impulse cytophotometric examinations were performed on fresh bladder tissue with carcinomas of different grades of malignancy and various depths of infiltration, and also on tissues with concomitant urothelial atypias. Cell kinetic examinations of urothelial atypias of mild, moderate, and severe grade revealed labeling indices comparable to those of urothelial carcinomas grade I, II, and III, respectively. The labeling indices of the carcinomas increased with both the grades of malignancy and the depth of invasion up to factor 5. Cytophotometrically mild atypias showed euploidy, while moderate to severe atypias revealed aneuploidy. By means of cytologic, cytophotometric, and cell kinetic analyses, two subgroups of G I urothelial carcinomas were distinguished. Subgroup I a corresponded to highly differentiated papillary urothelial carcinomas with low labeling indices, pap I-III differentiation, and euploidy. Subgroup I b, on the other hand, revealed pap differentiations of IV-V, aneuploidy, and higher labeling indices. This subgroup seems to be more prone to recurrences and apparently indicates higher grades of malignancy and depths of infiltration. The data presented provide evidence that a combination of these methods is helpful for early recognition of precursors of bladder cancer atypias as well as for exact evaluation of the biological potential of carcinomas.

Epithelial cells kinetics. A review of methods of study and their application to oral mucosa in health and disease. Part B. Comparison of cell kinetics in normal and abnormal epithelia

In Part A, the techniques most commonly used to study epithelial cell kinetics and their suitability for use in man are reviewed. In Part B, the application of such methods to comparative studies of normal and abnormal oral epithelial of both man and experimental animals is examined. Claims regarding the possible prognostic value of LI's or MI's of biopsies of potentially or overtly malignant human oral lesions are also considered. Normal and abnormal kinetic data for other lining epithelia, e.g., skin, uterine cervix and gastrointestinal mucosa are assessed where they provide a better illustration of some of the problems arising in such comparative investigations. Finally, the present and likely future areas in which cell kinetic studies may provide a guide to expected tumour prognosis and optimum treatment are summarized.

Enzymatic characteristics of tubular adenomas and carcinomas of the large intestine

Enzymes activities in homogenates of the large intestine were measured in biopsies from 11 tubular adenomas and six carcinomas and from the corresponding normal mucosa of each individual. A similar and significant increase was found in the total activities of glucose-6-phosphate dehydrogenase (G 6 PD), pyruvate kinase, and lactate dehydrogenase in adenomas and carcinomas as compared with the levels of normal mucosa. The lactate dehydrogenase isoenzyme patterns showed also a marked and similar change in the adenomas and carcinomas with a significant increase of lactate dehydrogenase M-monomers. Most of the adenomas showed slight to moderate dysplasia. The results indicate that the measurement of total G 6 PD, pyruvate kinase and lactate dehydrogenase activities for screening purposes has no predictive value in separating non-premalignant from premalignant adenomas. Moreover, it seems that the enzymatic characteristics of malignancy are present even in tubular adenomas. This is in agreement with the theory of a polyp-cancer sequence.

Epithelial cell kinetics--A review of methods of study and their application to oral mucosa in health and disease. Part A. Methods for studying cell proliferation and some sources of variation

Despite extensive investigation of cell kinetic parameters in wide range of normal and abnormal tissues and their potential value in understanding the pathogenesis of many disease states, as well as in prognosis and treatment planning, their application to oral epithelia remains limited. In part A the methods most commonly applied to the study of epithelial cell kinetics, i.e., isotope labelling, mitotic arrest and flow cytophotorimetry are reviewed with special emphasis on their technical limitations, sources of variation and inapplicability to humans in vivo. The ability of in vitro methods to reliably reproduce in vivo cell kinetic parameters is also considered. The application of cell kinetic studies to normal and abnormal oral tissues will be discussed in part B.

The biological significance of atypical hyperplasia of the prostate

In tissue biopsies and resection material (TUR) of the prostate a high coincidence (49.4%) was found between atypical primary hyperplasia with atypical-dysplastic microglandular, adenomatous and cribriform structures on the one hand and carcinomas on the other. The frequency of atypical hyperplasia in prostatic tissue without carcinoma was 2.8%. Microglandular pattern predominates in atypical hyperplasia combined with differentiated adenocarcinomas. A high coincidence between cribriformly structured glands of atypical primary hyperplasia and solid anaplastic-cribriform carcinomas can be observed. Autoradiographically the labeling index of atypical hyperplasia was three times as high as that of simple hyperplasia. The mean labeling index of atypical hyperplasia, however, was similar to that of poorly differentiated adenocarcinomas and cribriform carcinomas. The similar proliferation pattern of atypical hyperplasia and carcinomas as well as the high coincidence between both indicate that severe atypical primary hyperplasia is a precancerous lesion. Therefore, those patients with primary atypical hyperplasia with distinct cellular and structural atypia but without manifest carcinomas in prostatic biopsy or resection material should be followed up at short intervals.

Decreased rate of DNA-chain growth in human basal cell carcinoma

The DNA synthetic (S) phase of cell division is about twice as long in human basal cell carcinoma (BCC) as the normal epidermis and several non-malignant skin diseases. A similar increase in S phase duration seems to occur in tumours of the human oesophagus, larynx and recto-colon. At the molecular level, the overall rate of replication in a nucleus is determined by two factors--the frequency of initiation of replication and the rate of replication fork progression along the units of replication (for review see refs 7,8). Here we present evidence (based on DNA fibre autoradiography) that the observed increase in S phase duration may be due to a marked reduction in the rate of DNA replication along replication units, the density of simultaneously operating replication units remaining unchanged. This indicates an alteration in some biological component(s) of DNA synthesis in BCC that is of potential interest for characterizing the malignant transformation of the epidermal cell and that may perhaps be exploited therapeutically.

An analysis of the age distribution of colon cancer in adenomatosis coli

For the purpose of elucidating the genetic and environmental interaction in human carcinogenesis, the age distribution of colon cancer in adenomatosis coli (AC) patients in Japan and England were investigated and compated. According to the multiple mutation theory of carcinogenesis, the rate of tumor production is presented by a natural logarithm of the reciprocal of the survival fraction (the proportion on diagnosed colon cancer by age t either among AC patients or total colon cancer cases), and thus is given by a power function of t. The number of hits necessary for colon cancer development in AC patients was estimated to be 4.2 or 4.4 for males and 3.4 or 3.3 for females in Japanese cases, whereas it was 4.7 or 3.9 and 3.6 or 3.2, respectively, in English cases. The estimates are compatible between countries. On the other hand, from the age specific prevalence curve, number of hits in general population was estimated to be 5.0 for both sexes in Japan, which is approximately one hit less than the values for English general population, at least in males. The present results, when taking into account the geographic and/or chronologic variations in colon cancer frequency, suggest that the etiology of colon cancer in younger patients is primarily determined by a genetic predisposition whilst environmental factors are much more influential for the development of colon cancer in older patients.

Study of kinetics of epithelial cell populations in normal tissues of the rat's intestines and in carcinogenesis. II. Peculiarities of kinetics of enterocyte populations in experimental tumours of the colon

Cell proliferation in adenocarcinomas induced in the rat's colon by parenteral injection of 1,2-dimethylhydrazine was compared with that in normal colonic epithelium by means of autoradiographs. The distinct zone of proliferation, typical of the intestines, was not observed in the tumours, and cells replicated nearly in all segments of neoplasms. Tumour enterocytes were found to have a longer short mitotic cycle (16 instead of 11 hrs), due, chiefly, to an extension of G1-period duration. They were also characterized by a more pronounced heterogeneity as far as the values of ts and tG2 are concerned, and, probably, by the formation of an R2-population. Both the index of S-phase (29%) and labelled cell fraction (87%) after 6 injections of 3H-thymidine spaced at six-hour intervals, were lower in adenocarcinomas than in the zone of maximum proliferation in the descending colon (45 and 100%, respectively) and yet higher than the same parameters calculated for the whole population of the intestinal epithelium (17 and 60%, respectively). As far as proliferation parameters go, adenocarcinoma cells highly resemble those of the crypt bottom population in control animals, which was found to consist of several subpopulations with a varying mean duration of the mitotic cycle, and where stem enterocytes are likely to occur. When enterocytes become malignant, disturbances in their differentiation decrease cell shedding into the intestinal lumen and, thus, cause tumours to arise and develop.

Cell population kinetics of 1,2-dimethylhydrazine-induced colonic neoplasms and their adjacent colonic mucosa in the mouse

The parameters of cell population kinetics of symmetrical 1,2-dimethylhydrazine-induced colonic neoplasms and their adjacent colonic mucosa in the mouse were analyzed using the fraction labeled-mitoses curve method and compared with those of three groups of epithelial cells in the crypt of the descending colon of normal mouse. The analysis of three groups of epithelial cells in the crypt of normal mouse indicates that differentiation of epithelial cells was associated not only with a smaller proliferative pool of cells but also with a shortening of the duration of G2 phase and a prolongation of mitotic time. Other parameters of cell cycle did not change significantly. The mean cell cycle time of neoplastic cells in chemically induced colonic neoplasms was similar to that of epithelial cells in normal colon, but the variance was much greater in neoplastic cells. In neoplastic cells, the proliferative pool was greater, the G1 phase prlonged, and the S phase and the mitotic time became shorter as compared to epithelial cells in normal colon. The duration of G2 phase of neoplastic cells fell between the values of presumptive stem cells and differentiating cells in normal colon, compatible with the hypothesis that neoplastic cells are transformed stem cells defective in cellular differentiation. In the colonic mucosa immediately adjacent to neoplasms, the fraction-labeled-mitoses curve showed a flat second wave, indicating that the group of cells initially labeled by the pulse became a mixture of cells, some continuing the proliferative cycle normally, some going out of cycle, some slowing down in their passage from S through G2 to M, and some being arrested in mitotic phase. Such heterogeneous behavior of cells may be closely related to expansion of neoplasms. With some assumptions, however, cell cycle parameters of those normally cycling cells were estimated: the cell cycle time and the duration of G1 phase and mitotic phase were prolonged as compared to neoplastic cells and epithelial cells of normal colon.